As you can see he is saying that there is a huge security issue for anyone running macOS High Sierra: anyone can login to your root account without a password which will give them access to all areas of your mac and also allow them to have read and write privileges on other user accounts.

Apple will undoubtedly be working on a fix as this is something they won't want to leave for long. For now there is a fix which just needs you to create password for 'root'. You can do so by following the guide below.

Open System Preferences

Select Users & Groups

Click on the padlock in the bottom left

Enter your User Name and Password and click Unlock

Select Login Options

Select Join

Select Open Directory Utility...

Click on the padlock in the bottom left

Enter your User Name and Password and click Modify Configuration

Select Edit from your Menu Bar

Select Enable Root User

Enter a Password for root and then repeat the password and select OK

Root now has a password ensuring that it can't now be accessed without it.